1. Field of the Invention
The present invention generally relates to a transceiver device, in particular, to an echo cancellation technology of a transceiver device.
2. Description of Related Art
In communication systems, transceivers are usually employed for signal transmission. The transceiver is composed of a transmitter (TX) and a receiver (RX). FIG. 1 is a schematic view of a conventional full-duplex transceiver. Referring to FIG. 1, a near-end transceiver 102 and a far-end transceiver 104 are full-duplex transceivers. That is to say, the near-end transceiver 102 and the far-end transceiver 104 are capable of performing bi-directional data transmission through a transmission line 114. In addition, the near-end transceiver 102 includes a TX 106, an RX 108, and a hybrid circuit 116. The far-end transceiver 104 includes a TX 110, an RX 112, and a hybrid circuit 118.
As for the near-end transceiver 102, the TX 106 transmits a signal through the transmission line 114 to the RX 112 in the far-end transceiver 104. However, when the TX 106 in the near-end transceiver 102 transmits a signal to the far-end transceiver 104, if impedance mismatching occurs between the transmission line 114 and the transceivers 102, 104, an echo signal 120 is generated. The echo signal 120 is transmitted back to the RX 108 in the near-end transceiver 102, and the RX 108 regards the echo signal 120 as an interference noise. Therefore, an echo canceller (EC) is required to cancel the echo signal 120.
FIG. 2 is a schematic view of a conventional EC. Together referring to FIGS. 1 and 2, the EC is generally an adaptive finite impulse response (FIR) filter. (X1, X2, X3, X4, . . . , XM) is a transmitting data sequence of the EC. Delay units 202, 204, 206, 208, . . . , 210 are used to delay the input of the transmitting data sequence (X1, X2, X3, X4, . . . , XM). C1, C2, C3, C4, . . . , CM are tap coefficients. Amultiplier 212 is employed to multiply a tap X0 by a tap coefficient C0, and it is the same with multipliers 214 to 220. Then, an adder 222 is adopted to sum up the above products for generating an echo cancellation signal (Z1, Z2, Z3, Z4, . . . , ZM). The echo cancellation signal (Z1, Z2, Z3, Z4, . . . , ZM) is used for cancelling the echo signal 120.
As the echo signal 120 is transmitted for a distance twice the length of the transmission line 114, in order to cancel the echo signal 120 that has passed by such a long distance, the conventional EC may adopt multipliers at a number corresponding to the transmitting data sequence (X1, X2, X3, X4, . . . , XM) of the echo signal 120. Seen from the above, the conventional EC adopts a large number of multipliers, so that the cost is high and the total size of a chip is huge.